JSFiddle - React, Tailwind, and code Playground

HTML

<form name="ipForm" >
  UserName : <input type="text" name="userName"> 
</form>
<button id="html">get innerHTML</button>

JavaScript

document.getElementById("html").onclick = function() {
    var elems = document.getElementsByName("ipForm")[0]
                        .getElementsByTagName("input");

    for(var i = 0; i < elems.length; i++) {
        // set attribute to property value
        elems[i].setAttribute("value", elems[i].value);
    }
    
    alert(document.getElementsByName("ipForm")[0].innerHTML);
};